N-Ethyldiisopropylamine is an important amine which, being a strong base of low nucleophilicity, is used in elimination reactions and finds use as catalyst or auxiliary base in the organic synthesis of, for example, active ingredients (see, for example, WO 98/07430 A).
Chem. Ber. 91, pages 380-392 (1958), describes the synthesis of N-ethyldiisopropylamine by reaction of diisopropylamine with diethyl sulfate. This affords sulfates as unwanted by-products, which subsequently have to be disposed of in a costly and inconvenient manner.
The reaction of diisopropylamine with ethyl iodide for synthesis of N-ethyldiisopropylamine, described in J. Org. Chem. 16, pages 1911-1920, (1951) and U.S. Pat. No. 2,692,285 A, also leads to unwanted salts as by-products.
JP 10081650 A2, granted as JP 2851274 B2 (Koei Chem.), and JP 02180854 A2, granted as JP 2740828 B2 (Koei Chem.), especially describe the preparation of N-ethyldiisopropylamine from acetaldehyde and diisopropylamine or from acetone and ethylamine over Pd/C suspension catalysts in semi-batchwise mode at 20-200° C. and preferably 5-60 atm.
EP 1 020 424 A1 (BASF AG) describes a process for preparing N-ethyldiisopropylamine by reacting acetaldehyde with diisopropylamine and hydrogen at elevated temperature and under pressure in the presence of a hydrogenation catalyst, wherein the catalyst comprises an oxidic support material selected from the group of zirconium dioxide, titanium dioxide, aluminum oxide, silicon dioxide, zinc oxide, magnesium oxide, cerium dioxide, clays and zeolites or mixtures thereof. Preferred catalysts are, for example, Pd/Al2O3, Pt/ZrO2, Pd+Ag/SiO2, Ru/Al2O3, Pd/ZrO2.
WO 2007/137990 A1 (BASF AG) teaches processes for preparing an amine by reacting an aldehyde and/or ketone with hydrogen and a nitrogen compound selected from the group consisting of primary and secondary amines in the presence of a heterogeneous catalyst, wherein the reaction is carried out using a suspended catalyst as heterogeneous catalyst and is carried out in the semibatch mode in which the nitrogen compound as one reactant is placed in the reaction vessel and the aldehyde and/or the ketone as the other reactant is added during the course of the reaction and the aldehyde and/or the ketone is added in portions or continuously to the reaction mixture during the course of the reaction as a function of the achieved conversion of the nitrogen compound until a conversion of the nitrogen compound of at least 95% results, and all or part of the catalyst remains in the reaction vessel after the reaction batch and is reused for the next reaction batch.
One particular embodiment is the preparation of Hünig's base by reaction with acetaldehyde with diisopropylamine using a Pd/C suspension catalyst (loc. cit., bottom of page 14).